1. Field of the Invention
This invention relates to supermagnetostrictive alloys adapted for forming magnetostrictive elements to be used in devices for converting between magnetic energy and mechanical energy. More particularly, it is directed to rare earth-cobalt supermagnetostrictive alloys suitable for application in a wide range of temperatures including low temperatures of room temperature or below.
2. Description of the Related Art
It is known that magnetostriction, which is a strain caused when a magnetic field is applied externally to ferromagnetic substances such as Ni alloys, Fe-Co alloys, and ferrite, is applied to various devices such as magnetostrictive filters, magnetostrictive sensors, supersonic delay lines, magnetostrictive oscillators.
Recent developments in the field of instrumentation engineering and precision machinery require fine displacement control on the order of microns and thus demands that a displacement drive unit for the fine displacement control be developed. As a means for a drive mechanism of such a drive unit, attention has been given to the use of a device for converting between the magnetic and mechanical energy utilizing magnetostriction of a magnetostrictive substance.
However, conventionally known magnetostrictive materials (magnetostrictive substances) generally exhibit only a small displacement in absolute terms, thereby not being considered fully practicable. That is, conventional magnetostrictive materials are not satisfactory not only in terms of absolute drive displacement but also in terms of precision control as a displacement control drive means for which an accuracy in the order of microns is required.
On the other hand, as highly magnetostrictive materials, rare earth magnetostrictive alloys are disclosed, e.g., in the specification of U.S. Pat. No. 4,378,258 and Japanese Patent Examined Publication No. 33892/1987. However, rare earth-iron alloys are not satisfactory in that their magnetostriction is reduced at a low temperature range, nor are rare earth-cobalt alloys suitable for use in a high temperature environment because their Curie temperature is low. That is, the rare earth magnetostrictive alloys are, in general, not acceptable as a displacement control drive means that must be able to perform desired functions accurately in the order of microns in a wide range of temperatures from low (at room temperature) to high temperatures.
As an exception, TbFe.sub.2, whose easy axis of magnetization is &lt;111&gt; oriented among rare earth-iron alloys of the above type, is known to maintain and exhibit excellent magnetostriction at low temperatures (room temperature or lower). However, TbFe.sub.2 is not only inferior in oxidation resistance and sinterability but also disadvantageous in that it increases both the size and cost of the device as it requires a relatively large magnetic field in order to obtain a predetermined magnetostriction. Further, Tb(Fe.sub.0.8 Co.sub.0.2).sub.2, obtained by replacing part of Fe by Co is also known. This is a modification of TbFe.sub.2 with oxidation resistance and other properties improved and its easy axis of magnetization is also &lt;111&gt; oriented. However, Tb(Fe.sub.0.8 Co.sub.0.2).sub.2 is costly as a material and thus not economically advantageous as a general purpose material except for special applications.
It is, therefore, an object of this invention to provide a rare earth-cobalt supermagnetostrictive alloy that not only can maintain and exhibit excellent magnetostriction in a wide range of temperatures but also is relatively inexpensive and general purpose.
Another object of this invention is to provide a rare earth-cobalt supermagnetostrictive alloy suitable for use in displacement control drive means capable of functioning accurately in the order of microns.